Relationships between the controls of development and differentiation, and the processes of transformation and oncogenesis by chemical carcinogens: a) We will define the cellular and macromolecular aspects of the induction of squamous metaplasia. b) We will determine if induction of development of squamous metaplasia in mammary glands is similar to induction of squamous development and differentiation in other organ systems. c) We will determine the effects of the actions of chemical carcinogens on squamous metaplastic cells. d) We will elucidate the capability of precancerous mammary tissue to undergo induction of squamous metaplasia. The relevance of the mammary gland organ culture model to mammary gland tumorigenesis and its chemoprevention: a) We will test and extend previous evidence concerning whether mammary glands transformed by chemical carcinogens in culture can produce mammary tumors in mice. b) We will determine whether mammary glands whose chemical transformation was prevented by retinoid in culture are also prevented from producing mammary tumors in mice.